Ivermectin for Lice in Horses

Ivermectin is a popular de-wormer used for horses; however, if applied topically in powder form it can also be an effective treatment for lice. The two types of lice that affect horses are sucking lice and biting lice. Both are found throughout the entire United States.

  1. Sucking Lice

    • Sucking lice cause more problems for the horse since they can create anemia due to the loss of blood. This in turn can cause your horse to be weak. Growth in younger horses can be stunted if the lice are not destroyed relatively quickly.

    Biting Lice

    • Although biting lice do not cause anemia, they are quite irritating to the sensitive skin of the horse. Horses may bite at their own skin, continually scratch on posts or roll. Eventually there may be hair loss and open sores.

    Ivermectin

    • Ivermectin was first produced from a fungus--Streptomyces avermitilis--which was isolated from the soil in Japan. It was not licensed as an antibiotic for use on animals until 1984.

    Dosage and Application

    • Ivermectin should be administered in two to three doses, 10 days apart in order to break the life cycle of the lice. Dust the entire horse with the ivermectin powder and then brush the animal. If you have multiple horses, you should treat all of them at the same time since lice can easily transfer from one animal to another.

    Side Effefcts

    • Overdoses can produce toxic side effects such as seizures, coma, loss of control of the muscles, vomiting, depression, stupor and death. The American Board of Veterinary Toxicology (ABVT) claims, "Any species may be affected if the dose is large enough to penetrate the Blood-Brain-Barrier." Horses have not shown any adverse effects during reproduction while being treated with ivermectin for lice control; therefore, ivermectin can be safely used on stallions and brood mares. Unfortunately, there is not enough information to determine whether ivermectin is safe for foals under 4 months old.